Impulse-Radio Ultra-Wide-Band (IR-UWB) is different from conventional Narrow-Band (NB) and Wide-Band (WB) wireless technologies. Transmission in IR-UWB relies on the use of very short duration pulses e.g., smaller than 4 ns) and has average power spectral densities orders of magnitudes smaller than in other wireless systems.
In 2002, the United States Federal Communications Commission (FCC) specified a mask for bounding emissions from UWB transmitters to at least 500 MHz bandwidth in the 3.1-10.6 GHz range with average Power Spectral Densities (PSD) of −41.3 dBm/MHz in indoor environments. IR-UWB facilitates such low-power transmissions because of its use of low-duty cycle techniques applicable at the transmitters (e.g., 1 M pulse/s means at most 4 ns of duty cycle for each 1 μs offline). These low power transmissions make IR-UWB well suited for “tags” in sensor networks where low-cost and low-complexity are very important issues.
The most common schemes for implementing IR-UWB receivers rely on enemy detection with two pulse position modulation (2-PPM). In such schemes, information is transmitted according a time delay of UWB pulses in a constant pulse repetition interval (PRI). Accordingly, it is typically necessary to have a precise clock for timing acquisition and demodulation and to have dedicated units such as crystal oscillators, Phase-Locked-Loops (PLL), and Delay-Locked-Loops (DLL).
Unfortunately, however, precise clocks, crystal oscillators, Phase-Locked-Loops (PLL), and Delay-Locked-Loops (DLL) are typically area-consuming and power-greedy because they typically require large settling times and need to run during the entire data demodulation and synchronization period.